Dielectric lamination structure, manufacturing method of a dielectric lamination structure, and wiring board including a dielectric lamination structure

ABSTRACT

A dielectric structure comprising: a metal foil; a dielectric layer; and a conductor layer provided in this order, wherein the metal foil has a thickness of from 10 to 40 μm, the dielectric layer has a thickness of from 0.3 to 5 μm, and the conductor layer has a thickness of from 0.3 to 10 μm, the dielectric structure has plural vias which are separated from each other, and which penetrate through both of the dielectric layer and the conductor layer, and the vias of the dielectric layer have different diameters which are in a range of from 100 to 300 μm, a diameter of each of the vias of the conductor layer is larger than a diameter of a corresponding via of the dielectric layer by 5 to 50 μm, and a minimum via pitch is from 100 to 350 μm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dielectric lamination structure(dielectric stacked structure) and a wiring board having a dielectriclamination structure. More specifically, the invention relates to acapacitor incorporated in a wiring board as well as to such a wiringboard.

2. Description of the Related Art

In recent years, with the requirements of increase in functionality andreduction in size and weight on electronic equipment, the integrationdensity of electronic components such as ICs (integrated circuits) andLSIs (large scale integration) have increased rapidly and thoseelectronic components have come to operate at increasingly high speeds.With this trend, wiring boards which are mounted with electroniccomponents are required to be even higher in wiring density and haveeven more terminals than before.

Incidentally, in an IC which operates at high speed, when many devicesare switched simultaneously at high speed, an inductance componentbetween a power source and the IC obstructs high-speed operation of theIC because all of necessary high-frequency currents are supplied fromthe power source. As one countermeasure against this problem, that is,to supply the IC with charge necessary for its operation, a capacitor isprovided in a wiring board, whereby a local power source is provided inthe vicinity of the IC. Charge is stored in the capacitor in a DC senseand the capacitor stably supplies the IC with charge necessary for itsoperation.

A technique that a capacitor is incorporated in a wiring board (i.e.,“in the vicinity of” an IC) has been proposed. In this technique, thecapacitor is disposed inside an insulating resin layer of build-uplayers which are formed on a board core because disposing the capacitorcloser to the IC can make the wiring resistance and the inductancecomponent lower.

The insulating resin layer of the build-up layers is thin, it would benatural that the thickness of the capacitor which is disposed inside theinsulating resin layer be made small. However, if the capacitor wereunduly thin, it would become insufficient in rigidity to cause a warp,cracks, or the like. For example, this raises a problem that the processof incorporating the capacitor into the wiring board becomes difficultto execute. For example, JP-A-2004-134806 (corresponding to EP 1 408 520A2) discloses a structure which is produced by forming a firstthick-film dielectric having through-holes on a metal foil, then forminga first electrode having through-holes on the dielectric by screenprinting, and finally firing the metal foil, the first thick-filmdielectric, and the first electrode at the same time. This structure canprevent development of cracks and separation of the dielectric and thefirst electrode due to the difference in thermal expansion coefficientwhen the dielectric and the first electrode are fired at the same time.

3. Problems to be Solved by the Invention

However, the technique of JP-A-2004-134806 (corresponding to EP 1 408520 A2), which uses the thick-film dielectric, cannot preventdevelopment of cracks and separation which are caused by a warp or thelike of the capacitor itself which occurs due to, for example, thedifference between the thermal expansion coefficients of the capacitorand the insulating resin layer of the build-up layers in the case wherea thin dielectric is formed so that the capacitor is incorporated in awiring board. Furthermore, the use of the thick-film dielectric iscontrary to the requirement of reduction in size and weight. If thecapacitor has an entirely flat structure, peeling may occur at theboundary between the insulating resin material and the capacitor whenthe capacitor is incorporated into (mounted on) the insulating resinlayer of the build-up layers. In addition, there may occur an event thatair bubbles enter the boundary between the capacitor and the insulatingresin material at the time of mounting.

Where the first electrode is formed on the dielectric by screenprinting, there may occur an event that a printing mask for formation ofthe first electrode is deviated from the dielectric and, resultingly,conductor paste to form the first electrode goes into the through-holesof the dielectric to render the metal foil and the first electrodeelectrically continuous with each other. This raises a problem that suchan event lowers the production yield and makes it impossible to securesufficient reliability of the capacitor.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances,and an object of the invention is therefore to provide a highly reliabledielectric lamination structure which is not prone to warp even if, inparticular, a thin capacitor is formed and makes it easier to execute aprocess of incorporating a capacitor into an insulating resin layer ofbuild-up layers, a manufacturing method of a dielectric laminationstructure capable of increasing the production yield and manufacturing ahighly reliable dielectric lamination structure, and a wiring boardhaving such a dielectric lamination structure.

To solve the above problems, the invention provides a dielectriclamination structure in which a dielectric layer and a conductor layerare provided in this order on at least one surface of a metal foil,characterized in:

that the thickness of the metal foil is 10 to 40 μm, the thickness ofthe dielectric layer is 0.3 to 5 μm, and the thickness of the conductorlayer is 0.3 to 10 μm;

that plural vias which are separated from each other penetrate throughboth of the dielectric layer and the conductor layer in a thicknessdirection; and

that the vias of the dielectric layer have different diameters which arein a range of 100 to 300 μm, the diameter of each of the vias of theconductor layer is larger than the diameter of a corresponding via ofthe dielectric layer by 5 to 50 μm, and a minimum via pitch is in arange of 100 to 350 μm.

Usually, when a dielectric lamination structure is mounted on(incorporated in) an insulating resin layer of build-up layers, it isput on the insulating resin layer while being pressed against the latterto some extent and the dielectric lamination structure is warped by thepressing. In particular, cracks may develop in the dielectric layer. Onthe other hand, in the invention, since the dielectric laminationstructure is formed by laminating the dielectric layer and the conductorlayer on the metal foil which is 10 to 40 μm in thickness, the metalfoil is relatively high in rigidity. As a result, the dielectriclamination structure is made flat and given sufficient flexibility. Whenthe dielectric lamination structure is mounted on an insulating resinlayer of build-up layers, development of cracks or the like due topressing can be prevented. Furthermore, since the dielectric layer is asthin as 0.3 to 5 μm and the conductor layer is as thin as 0.3 to 10 μm,the dielectric lamination structure can easily be incorporated in aninsulating resin layer of build-up layers and a sufficient capacitancecan be secured.

The plural vias which are separated from each other penetrates throughboth of the dielectric layer and the conductor layer. Therefore, whenthe dielectric lamination structure is mounted on an insulating resinlayer of build-up layers, the contact area is larger, by the sum of theareas of the inside surfaces of the vias, than, for example, in a casethat the surface that is in contact with an insulating resin layer ofbuild-up layers or the like is completely flat. The adhesion isincreased accordingly and an event that the dielectric laminationstructure is peeled off due to warping or the like of the wiring boardcan be avoided. It is preferable that the vias of the dielectric layerhave different diameters which are in a range of 100 to 300 μm. In thiscase, it is preferable that the diameter of each of the vias of theconductor layer be larger than the diameter of a corresponding via ofthe dielectric layer by 5 to 50 μm. It is also preferable that theminimum one of via pitches of the vias be in a range of 100 to 350 μm.If the diameter of the vias of the dielectric layer is not larger thanor equal to 100 μm, the vias are too small to provide sufficientadhesion. If the difference between the diameter of each via of thedielectric layer and that of the corresponding via of the conductorlayer does not satisfy the condition 5 to 50 μm, portions of theconductor layer may pass the dielectric layer and brought into contactwith the metal foil. On the other hand, if the vias of the dielectriclayer is larger than 300 μm and the diameter of each via of theconductor layer is larger than that of the corresponding via of thedielectric layer by more than 50 μm, the area of the conductor layerbecomes too small to secure a sufficient capacitance. Setting theminimum via pitch in the range of 100 to 350 μm makes it possible toarrange the vias without causing short-circuiting.

The dielectric lamination structure according to the invention may besuch that through-holes penetrate through the metal foil in thethickness direction so as to communicate with the respective vias, andthat the diameter of each of the through-hole is smaller than thediameter of a corresponding via of the dielectric layer. In theinvention, the vias and the through-holes which communicate with eachother are formed in the dielectric lamination structure. Therefore, whenthe dielectric lamination structure is mounted on a dielectric resinlayer of build-up layers, air etc. located in between are guided toabove the dielectric lamination structure via the through-holes, wherebyentrance of air bubbles etc. into the boundary between the dielectriclamination structure and the dielectric resin layer of the build-uplayers can be suppressed. Without intervention of air bubbles etc., theadhesion between the dielectric lamination structure and the dielectricresin layer of the build-up layers is increased and peeling of thedielectric lamination structure can be prevented. Since the diameter ofeach combination of a through-hole and a via increases stepwise from themetal foil to the conductor layer, it becomes easier for, for example,the insulating resin layer of the build-up layers to go into the insidesof the through-holes.

In the dielectric lamination structure according to the invention, thepositional deviation between the center of each of the vias of thedielectric layer and the center of a corresponding via of the conductorlayer may be less than or equal to 10 μm. In the invention, since thepositional deviation between the center of each via of the dielectriclayer and the center of a corresponding via of the conductor layer isless than or equal to 10 μm, the length d₂ of retreat of the sidesurface 4 a ₁ from the side surface 3 a ₁ (see FIG. 13) is made uniformamong all side surfaces 4 a ₁ and a sufficient distance (insulationdistance) can be secured reliably between the metal foil and theconductor layer. This makes it possible to provide a highly reliabledielectric lamination structure.

In the dielectric lamination structure according to the invention, thedielectric layer and the conductor layer may be provided on both sidesof the metal foil (thus, a conductor layer, a dielectric layer, themetal foil, a dielectric layer, and a conductor layer are provided inthis order) so as to be arranged symmetrically with respect to the metalfoil. In the invention, since the dielectric layer and the conductorlayer may be provided on both surfaces of the metal foil, the influenceon the metal foil of sintering contraction of the dielectric layerswhich occurs at the time of firing is reduced and warping or deformationof the dielectric lamination structure is suppressed. Arranging thedielectric layers symmetrically with respect to the metal foil iseffective in further suppressing warping of the dielectric laminationstructure which otherwise tends to occur at the time of firing.

In the dielectric lamination structure according to the invention, themetal foil may be an Ni foil. Where the metal foil is an Ni foil, themetal foil is given high rigidity and the dielectric laminationstructure is made flat and sufficiently flexible, which makes itpossible to prevent development of cracks or the like due to pressingwhich is performed when the dielectric lamination structure is mountedon an insulating resin layer of build-up layers. Examples, other thanNi, of the material of the metal foil are tungsten, copper, gold,platinum, and palladium. Among these materials, Ni is most appropriatein terms of the firing conditions, conductivity, and cost.

In the dielectric lamination structure according to the invention, theconductor layer may contain ceramic powder at 50 vol % or less. In theinvention, since the conductor layer contains ceramic powder, theadhesion between the conductor layer and the dielectric layer isincreased. In the dielectric lamination structure according to theinvention, the ceramic powder contained in the conductor layer may havethe same composition as ceramics as a material of the dielectric layer.Using, as the ceramic powder, a material having the same composition asceramics as the material of the dielectric layer can further increasethe adhesion. If the conductor layer contains the ceramic powder at morethan 50 vol %, reduction in conductivity (increase in resistivity) orreduction in flexibility may occur after firing.

The dielectric layer is made of dielectric ceramics such as bariumtitanate, lead titanate, or strontium titanate. Alternatively, thedielectric layer may be made of low-temperature-fired ceramics such asglass ceramics obtained by adding an inorganic ceramic filler toborosilicate glass or lead borosilicate glass. As a further alternative,to attain required characteristics, the dielectric layer may be made ofhigh-temperature-fired ceramics such as alumina, aluminum nitride, boronnitride, silicon carbide, or silicon nitride.

The dielectric lamination structure according to the invention, maybesuch as to be deformed in a radius-of-curvature range of 5 to 500 mmwhen a prescribed jig is pressed against the dielectric laminationstructure directly or indirectly from the side of the conductor layer ina state that the conductor layer is an outermost layer.

In the invention, the dielectric lamination structure having suchflexural strength as to satisfy the above condition is highly flexibleand hence is not prone to cracks or the like which may otherwise developin a process of mounting the dielectric lamination structure on aninsulating resin layer of build-up layers or due to warping of a wiringboard. As such, the dielectric lamination structure can be made highlyreliable.

A wiring board according to the invention incorporates the dielectriclamination structure having the above-described workings and advantages.The wiring board is provided with an insulating resin layer which coversthe dielectric lamination structure, and an electrode layer andthickness-direction conductors which electrically connect the electrodelayer and the conductor layer are formed on at least a front surface ofthe insulating resin layer. Therefore, the dielectric laminationstructure can be integrally incorporated in the wiring board as part ofa capacitor. Since the thickness-direction conductors are arranged inarray form, the wiring length can be shortened in implementation andhigh-density implementation is thus enabled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary dielectric laminationstructure according to the present invention.

FIG. 2 is a sectional view of the exemplary dielectric laminationstructure according to the invention.

FIG. 3 is a sectional view of a capacitor according to the invention.

FIG. 4 is a sectional view of an exemplary wiring board according to theinvention.

FIG. 5 is explanatory diagrams showing manufacturing steps of thedielectric lamination structure according to the invention.

FIG. 6 is explanatory diagrams showing manufacturing steps of thecapacitor following the steps of FIG. 5.

FIG. 7 is explanatory diagrams showing manufacturing steps of thecapacitor following the steps of FIG. 6.

FIG. 8 is a sectional view of a capacitor according to another (second)embodiment of the invention.

FIG. 9 is explanatory diagrams showing manufacturing steps of thecapacitor according to the second embodiment.

FIG. 10 is explanatory diagrams showing manufacturing steps of thecapacitor following the steps of FIG. 9.

FIG. 11 is explanatory diagrams showing manufacturing steps of thecapacitor following the steps of FIG. 10.

FIG. 12 is a conceptual diagram showing a measuring method.

FIG. 13 is a plan view of the exemplary dielectric lamination structureaccording to the invention.

FIG. 14A is a photograph showing the state of the side surface of athrough-hole of a pre-firing metal foil used in the dielectriclamination structure according to the invention.

FIG. 14B is a photograph showing the state of the side surface of athrough-hole of a post-firing metal foil used in the dielectriclamination structure according to the invention.

FIGS. 15A, 15B and 15C show another manufacturing process of adielectric lamination structure.

DESCRIPTION OF REFERENCE NUMERALS

Reference numerals used to identify various structural features in thedrawings include the following.

-   1: Dielectric lamination structure-   2: Metal foil (inner electrode layer)-   2 a: Through-hole-   3: Dielectric layer-   3 a: Via-   4: Conductor layer (inner electrode layer)-   4 a: Via-   5: Communication hole-   6, 7: Outer electrode layer-   8, 8 a, 8 b, 8 c, 9: Via conductor (via, thickness-direction    conductor)-   10, 50: Capacitor-   16, 17: Insulating resin layer-   100: Wiring board

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be hereinafter described withreference to the accompanying drawings.

FIG. 1 is a perspective view of a dielectric lamination structure 1according to the invention. FIG. 2 is a sectional view of the dielectriclamination structure 1 according to the invention. FIG. 3 is a schematicsectional view of a capacitor 10 according to the invention. In thisembodiment, it is assumed that a first major surface and a second majorsurface of a plate-like member shown in a figure are the top surface andthe bottom surface in the figure, respectively. (In the followingdescription, the top dielectric layer will be called “first dielectriclayer 3” and the bottom dielectric layer will be called “seconddielectric layer 3′.” The terms “first conductor layer 4” and “secondconductor layer 4′” will be used in a similar manner.)

As shown in FIGS. 1 and 2, the dielectric lamination structure 1 isprovided with a metal foil (inner electrode layer) 2 which is made of ametal such as nickel, first and second dielectric layers 3 and 3′ whichare made of, for example, high-permittivity ceramics such as bariumtitanate (BaTiO₃; hereinafter may be abbreviated as “BT”), and first andsecond conductor layers (inner electrode layers) 4 and 4′ which are madeof a metal such as nickel. The first dielectric layer 3 and the firstconductor layer 4 are laminated on the front surface of the metal foil 2in this order, and the second dielectric layer 3′ and the secondconductor layer 4′ are laminated on the back surface of the metal foil 2in this order. The metal foil 2 is thus electrically insulated from thefirst and second conductor layers 4 and 4′. The dielectric laminationstructure 1 has a plate-like form which is square or rectangular in aplan view.

In the dielectric lamination structure 1, plural communication holes 5are provided in a prescribed pattern each of which consists of athrough-hole 2 a formed in the metal foil 2, vias 3 a and 3 a′ formed inthe respective dielectric layers 3 and 3′, and vias 4 a and 4 a′ formedin the respective conductor layers 4 and 4′, has a circular shape in aplan view, and extends in the thickness direction. The communicationholes 5 are classified into several groups having different diameters.The diameter of each communication hole 5 increases stepwise in thedirections from the metal foil 2 to the first and second conductorlayers 4 and 4′ past the first and second dielectric layers 3 and 3′.The first and second dielectric layers 3 and 3′ are formed symmetricallywith respect to the metal foil 2 in a sense that the communication holes5 are included. The first and second conductor layers 4 and 4′ are alsoformed symmetrically in the same manner. Only one of the combination ofthe first dielectric layer 3 and the first conductor layer 4 and thecombination of the second dielectric layer 3′ and the second conductorlayer 4′ may be formed on one surface of the metal foil 2. However,forming the first and second dielectric layers 3 and 3′ and the firstand second conductor layers 4 and 4′ symmetrically on both of the frontand back surfaces of the metal foil 2 can suppress warping whichotherwise tends to occur due to the difference between the thermalexpansion coefficients of the metal foil 2 and the first and seconddielectric layers 3 and 3′ at the time of simultaneous firing, forexample.

As shown in FIG. 3, the capacitor 10 is provided with the dielectriclamination structure 1 (core member), insulating resin layers 16 whichcover the dielectric lamination structure 1, a first outer electrodelayer 6 formed on a first major surface 10 a of the capacitor 10, asecond outer electrode layer 7 formed on a second major surface 10 b ofthe capacitor 10, via conductors 8 (8 a, 8 b, and 8 c) which penetratethrough the capacitor 10 in the thickness direction and electricallyconnect the first and second outer electrode layers 6 and 7, and viaconductors 9 which penetrate through the insulating resin layer 16 fromthe first major surface 10 a to the first conductor layer 4 andelectrically connect the first outer electrode layer 6 and the firstconductor layer 4. Although not shown in FIG. 3, the capacitor 10 isalso formed with a dielectric lamination structure (dummy capacitor) inwhich the first conductor layer 4 is not electrically continuous withthe via conductors 9. With the above structure, the adhesion which isnecessary when the capacitor 10 is mounted on a wiring board 100 (seeFIG. 4; described later) is increased and peeling of the capacitor 10off the wiring board 100 can be prevented or suppressed.

The first and second outer electrode layers 6 and 7 are used as a powersupply electrode, a grounding electrode, or a signal transmissionelectrode, for example, and are electrically connected to each other viathe via conductors 8.

The via conductors 8, which are inserted in the respective communicationholes 5, include a via conductor(s) 8 a which is electrically connectedto the metal foil 2 which is one inner electrode layer and a viaconductor(s) 8 b which is electrically insulated from the metal foil 2and electrically connected, via the first outer electrode layer 6, tothe first conductor layer 4 which is another inner electrode layer. Asignal transmission via conductor(s) 8 c may further be provided whichis electrically insulated from the metal foil 2 and the first and secondconductors 4 and 4′. The via conductors 8 a, 8 b, and 8 c have the samediameter. More specifically, as mentioned above the communication holes5 are classified into several groups having different via diameters, andthe diameter of the via conductors 8 a, 8 b, and 8 c corresponds to theminimum one of the diameters of the through-holes 2 a of the metal foil2. Therefore, the via conductor(s) 8 a is electrically connected to themetal foil 2 and the via conductors 8 b and 8 c are electricallyinsulated from the metal foil 2 merely by forming (inserting) the viaconductors 8 a, 8 b, and 8 c in the communication holes 5. The diameterof each communication hole 5 increases in the directions from the metalfoil 2 to the first and second conductor layers 4 and 4′ (in otherwords, the diameters of the vias 4 a and 4 a′ are larger than thediameter of the through-hole 2 a of the metal foil 2). Therefore, whenthe via conductor(s) 8 a is formed, it can be electrically insulatedfrom the first and second conductor layers 4 and 4′.

The plural via conductors 9 are provided for the first conductor layer 4in array form.

Next, a wiring board 100 incorporating the above-configured capacitor 10will be described. FIG. 4 is a schematic sectional view showing theconfiguration of the wiring board 100. The wiring board 100 isconfigured in such a manner that first and second core conductor layersM1 and M11 as wiring metal layers having prescribed patterns are formedon first and second major surfaces MP1 and MP2, respectively, of a boardcore 12 which is a heat-resistant resin plate (e.g., bismaleimidetriazine resin plate), a fiber-reinforced resin plate (e.g.,glass-fiber-reinforced epoxy resin plate), or the like. The first andsecond core conductor layers M1 and M11 are formed as surface conductorpatterns for covering the first and second major surfaces MP1 and MP2 ofthe board core 12, and are used as a power supply layer or a groundinglayer. On the other hand, through-holes are formed through the boardcore 12 with drills, for example, and through-hole conductors 30 forelectrically connecting the first and second core conductor layers M1and M11 are formed in the respective through-holes.

Plural insulating resin layers 16 (V1-V3) and 26 (V11-V13) which aremade of a thermosetting resin composition, for example, are formed onthe surfaces of the first and second core conductor layers M1 and M11.Furthermore, conductor layers M2-M4 and M12-M14 having metalinterconnections are formed between the insulating resin layers 16(V1-V3) and 26 (V11-V13) by Cu plating, for example. The first coreconductor layer M1 and the conductor layer M2 are connected to eachother by via conductors 34, and the second core conductor layer M11 andthe conductor layer M12 are connected to each other by via conductors 35(interlayer connections). Likewise, the conductor layers M2-M4 areconnected to each other by via conductors 34, and the conductor layersM12-M14 are connected to each other by via conductors 35. The conductorlayer M4 formed on the surface of the topmost insulating resin layer 16(V3) has metal terminal pads 25, and the conductor layer M14 formed onthe bottommost insulating resin layer 26 (V13) has metal terminal pads27. The via conductors 34 and 35 formed through the respectiveinsulating resin layers 16 (V3) and 26 (V13) are what is called filledvias formed by filling via holes by Cu plating, for example. The viaconductors 34 and 35 may be of other types; for example, they may bewhat is called conformal vias having via pads which are provided on thebottom surface side so as to be electrically continuous with the viaconductors 34 and 35 and via lands which are provided on the oppositeside so as to project outward from the opening peripheries of the viaconductors 34 and 35.

The wiring board 100 incorporates the capacitor 10 in a central portionof the insulating resin layer 16 (V2) which is formed on the board core12. The capacitor 10 is provided within the thickness of the insulatingresin layer 16 (V2), and the capacitor 10, more specifically, the firstand second outer electrode layers 6 and 7 and the first and second majorsurfaces 10 a and 10 b are in close contact with the adjacent insulatingresin layers 16. The conductor layers M2 and M3 may be formed so as toinclude the first and second outer electrode layers 6 and 7 of thecapacitor 10, respectively, and the insulating resin layer 16 (V2) ofthe wiring board 100 may be formed so as to include the insulating resinlayer 16 of the capacitor 10. In this case, the build-up layers and thecapacitor 10 are integrated with each other, and hence the top surfaceof the capacitor 10 can easily be made flat and the build-up layers canbe made stable.

On the first major surface MP1 of the board core 12, the core conductorlayer M1, the conductor layers M2-M4, and the insulating resin layers 16(V1-V3) form a first wiring lamination portion L1. On the second majorsurface MP2 of the board core 12, the core conductor layer M11, theconductor layers M12-M14, and the insulating resin layers 26 (V11-V13)form a second wiring lamination portion L2. Each of the first and secondwiring lamination portions L1 and L2 is formed by laminating theinsulating resin layers and the conductor layers alternately so that thesurface of the outermost insulating resin layer 16 becomes a first orsecond major surface CP1 or CP2. The plural metal terminal pads 25 areformed on the first major surface CP1, and the plural metal terminalpads 27 are formed on the second major surface CP2. The metal terminalpads 25 on the side of the first wiring lamination portion L1 serve assolder lands for flip chip connection of an integrated circuit chip orthe like. The metal terminal pads 27 on the side of the second wiringlamination portion L2 are used as back surface lands (PGA pads or BGApads) for connecting the wiring board 100 itself to a mother board orthe like via a pin grid array (PGA) or a ball grid array (BGA).

The metal terminal pads 25 as the solder lands are arranged in the formof lattice points (i.e., in array form) in a central region of the firstmajor surface CP1 of the wiring board 100, and form a chip mountingportion together with solder bumps 21 formed thereon. The metal terminalpads 27 as the back surface lands are also arranged in the form oflattice points (i.e., in array form) on the second major surface CP2.Solder resist layers 18 and 28 (SR1 and SR11) made of a photosensitiveor thermosetting resin composition are formed on the outermost conductorlayers M4 and M14, respectively. To expose parts of the metal terminalpads 25 as the solder lands and parts of the metal terminal pads 27 asthe back surface lands, exposing holes 18 a and 28 a are formed throughthe solder resist layers 18 and 28 so as to be in one-to-onecorrespondence with the metal terminal pads 25 and 27. The solder bumps21 in the solder resist layer 18 which is formed on the side of thefirst wiring lamination portion L1 may be made of solder containingsubstantially no Pb such as Sn—Ag, Sn—Cu, Sn—Ag—Cu, or Sn—Sb. On theother hand, the metal terminal pads 27 which are formed on the side ofthe second wiring lamination portion L2 are formed so as to be partiallyexposed in the exposing holes 28 a of the solder resist layer 28. In thewiring board 100, signal transmission paths are formed so as to extendfrom the metal terminal pads 25 which are formed on the side of thefirst major surface MP1 of the board core 12 (i.e., on the side of thefirst wiring lamination portion L1) to the metal terminal pads 27 whichare formed on the side of the second major surface MP2 (second wiringlamination portion L2).

The thus-described wiring board 100 can be manufactured by forming thefirst and second wiring lamination portions L1 and L2 on the first andsecond major surfaces MP1 and MP2 of the board core 12, respectively, bya known build-up method or the like. Before executing a build-up processto form the first and second wiring lamination portions L1 and L2,through-holes are formed through the board core 12 and the through-holeconductors 30 are formed in the through-holes by Cu plating or the like.A manufacturing method of the wiring board 100 will be described belowtogether with a manufacturing method of the capacitor 10.

FIGS. 5-7 are explanatory diagrams showing a manufacturing process ofthe dielectric lamination structure 1 and the capacitor 10. First, asshown in FIG. 5 (5-1), a metal foil of nickel or the like which, forexample, measures 150 mm×150 mm and is 10 to 40 μm in thickness isprepared and plural through-holes 2 a are formed in a prescribed patternso as to be separated from each other by etching such as wet etching.The through-holes 2 a may be formed by laser light instead of etching.The through-holes 2 a are formed so that the minimum one of their viapitches P falls within a range of 100 to 350 μm and that they correspondto vias 3 a and 3 a′ which will be formed in first and second dielectriclayers 3 and 3′ at different diameters which fall within a range of 100to 300 μm (described later).

Then, pre-firing barium titanate green sheets, which measure 150 mm×150mm and are 0.3 to 5 μm in thickness and which will become first andsecond dielectric layers 3 and 3′ after firing, are laid on both of thefront and back surfaces of the metal foil 2 having the through-holes 2a, and are pressure-bonded to the metal foil 2 under prescribedconditions. The barium titanate green sheets are obtained by formingthin-films of barium titanate slurry on carrier sheets 3 s and 3 s′ ofpolyester or the like by a known doctor blade method and drying the thinfilms. The barium titanate green sheets are laid on both of the frontand back surfaces of the metal foil 2 and pressure-bonded to the metalfoil 2 under prescribed conditions, and then the carrier sheets 3 s and3 s′ are peeled off.

Then, as shown in FIG. 5 (5-2), pre-firing nickel green sheets, whichmeasure 150 mm×150 mm and are 0.3 to 10 μm in thickness and which willbecome first and second conductor layers 4 and 4′ after firing, are laidon the first and second dielectric layers 3 and 3′, respectively. Thenickel green sheets are obtained by forming thin-films of nickel slurryon carrier sheets 4 s and 4 s′ of polyester or the like by a knowndoctor blade method and drying the thin films. The nickel green sheetsare laid on the surfaces of the barium titanate green sheets andpressure-bonded to them under prescribed conditions, and then thecarrier sheets 4 s and 4 s′ are peeled off (see FIG. 5 (5-3)). A ceramicpowder of, for example, barium titanate, which is contained in the firstand second dielectric layers 3 and 3′, may be mixed into the slurry forforming the nickel green sheets at 50 vol % or less. Mixing the samecomponent as the first and second dielectric layers 3 and 3′ are made ofinto the first and second conductor layers 4 and 4′ can further increasethe adhesion when the first and second dielectric layers 3 and 3′ andthe first and second conductor layers 4 and 4′ are fired at the sametime. If the ceramic powder were mixed at more than 50 vol %, reductionin conductivity (i.e., increase in resistivity), reduction inflexibility, or a like phenomenon may occur after the firing. The firstand second dielectric layers 3 and 3′ and the first and second conductorlayers 4 and 4′ may be laminated on the metal foil 2 by pressure-bondingthe former to the latter after laying the former on the latter.

Then, as shown in FIG. 5 (5-4), vias 3 a and 3 a′ and vias 4 a and 4 a′are formed through the first and second dielectric layers 3 and 3′ andthe first and second conductor layers 4 and 4′ in the thicknessdirection from both sides by, for example, a method using laser light atthe positions corresponding to the through-holes 2 a of the metal foil2. Where each set of vias 3 a, 3 a′, 4 a, and 4 a′ is formed through thefirst and second dielectric layers 3 and 3′ and the first and secondconductor layers 4 and 4′ simultaneously by laser light, the portionsconcerned of the first and second conductor layers 4 and 4′ are meltedearlier than the portions concerned of the first and second dielectriclayers 3 and 3′ because the melting point of the former is lower thanthat of the latter, whereby the via diameter D₂ of the first and secondconductor layers 4 and 4′ becomes larger than the via diameter D₁ of thefirst and second dielectric layers 3 and 3′.

It is preferable that the diameter D₁ of each pair of vias 3 a and 3 a′be larger than the diameter D₀ of the corresponding through-hole 2 a andfall within a range of 100 to 300 μm. It is preferable that the diameterD₂ of the corresponding pair of vias 4 a and 4 a′ be larger than thediameter D₁ of the pair of vias 3 a and 3 a′ by 5 to 50 μm (D₁+5μm≦D₂≦D₁+50 μm). Making each pair of vias 4 a and 4 a′ of the first andsecond conductor layers 4 and 4′ wider than the corresponding pair ofvias 3 a and 3 a′ of the first and second dielectric layers 3 and 3′makes it possible to electrically insulate the metal foil 2 from thefirst and second conductor layers 4 and 4′ in a reliable manner.

It is preferable that the diameter D₁ of each pair of vias 3 a and 3 a′be larger than the via diameter D₀ of the corresponding through-hole 2 aby 10 to 40 μm (D₁+10 μm≦D₂≦D₁+40 μm), for the following reasons. If thediameter difference were smaller than 10 μm, laser light would alsoshine on the first and second dielectric layers 3 and 3′ when viathrough-holes 8 h to be used for forming via conductors 8 (describedlater) are formed, as a result of which cracks or the like might developin the first and second dielectric layers 3 and 3′. If the diameterdifference were larger than 40 μm, the area of the first and secondconductor layers 4 and 4′ would become smaller than a desired value, asa result of which the capacitance might become smaller than a desiredvalue.

Then, as shown in FIG. 6 (6-1 and 6-2), the thus-obtained structure iscut into, for example, 15-mm-square sections by a cutting machine (notshown) and those sections are subjected to degreasing and firing underprescribed conditions, whereby dielectric lamination structures 1 havingcommunication holes 5 which are formed in a prescribed pattern areproduced.

Then, as shown in FIG. 6 (6-3), each of the thus-obtained dielectriclamination structures 1 is mounted at a prescribed position in the firstwiring lamination portion L1 of a wiring board 100 which was formed by aknown build-up method, for example.

More specifically, as shown in FIG. 7 (7-1), in an in-process wiringboard 100, an insulating resin layer 16 (V1), via conductors 34, and aconductor layer M2 are formed by a known build-up method. At this time,the conductor layer M2 is formed in a prescribed pattern so that it willbecome a second outer electrode layer 7 of a capacitor 10 when thedielectric lamination structure 1 is mounted. Then, an insulating resinlayer 16 (V2 a) made of a thermosetting resin composition or the like isformed on the insulating resin layer 16 (V1) and the conductor layer M2.Then, the dielectric lamination structure 1 is mounted on the insulatingresin layer 16 (V2 a) by a mounter (not shown). At this time, since thedielectric lamination structure 1 is mounted in a state that theinsulating resin layer 16 (V2 a) has not been set at all or has been sethalfway, the dielectric lamination structure 1 can be mounted bypressure-bonding it to the insulating resin layer 16 (V2 a) as formedwhich is flat. Portions of the insulating resin layer 16 (V2 a) rise(flow up) relatively into the communication holes 5, and are thereby gointo and attached to the lower portions of the communication holes 5(i.e., the vias 3 a′ of the second dielectric layer 3′ and the vias 4 a′of the second conductor layer 4′). An alternative method is such thatthe insulating resin layer 16 (V2 a) is set, a separate adhesive or thelike is applied to it, and then the dielectric lamination structure 1 isput thereon. On the other hand, the dielectric lamination structure 1 ismounted on the insulating resin layer 16 (V2 a) while being pressedagainst the insulating resin layer 16 (V2 a). However, since thedielectric lamination structure 1 is provided with the metal foil 2which is high in rigidity, no warp, cracks, or the like occur in thedielectric lamination structure 1. Furthermore, since the dielectriclamination structure 1 is provided with the plural communication holes 5which extend in the thickness direction, air etc. existing between thedielectric lamination structure 1 and the insulating resin layer 16 (V2a) are guided to above the dielectric lamination structure 1 via thecommunication holes 5, whereby entrance of air bubbles is prevented andthe dielectric lamination structure 1 can be mounted easily. Stillfurther, the communication holes 5 increase the area of contact betweenthe dielectric lamination structure 1 and the insulating resin layer 16(V2 a), as a result of which the adhesion between them is increased andsuch trouble as peeling can be avoided.

Then, as shown in FIG. 7 (7-2), an insulating resin layer 16 (V2 b) madeof a thermosetting resin composition or the like is formed so as tocover the dielectric lamination structure 1.

Then, as shown in FIG. 7 (7-3), via holes 8 h and 9 h are formed throughthe insulating resin layers 16 (V2 a) and 16 (V2 b) at prescribedpositions by laser light.

Subsequently, as shown in FIG. 7 (7-4), via conductors 8 and 9 areformed by filling the thus-formed via holes 8 h and 9 h by Cu plating orthe like and a conductor layer M3, which will become a first outerelectrode layer 6, is formed in a prescribed pattern. More specifically,the insides of the via holes 8 h and 9 h and the surface of theinsulating resin layer 16 (V2 b) are subjected first to Cu electrolessplating and then to Cu electroplating. Then, via conductors 8 and 9 anda conductor layer M3 including a first outer electrode layer 6 areformed by forming an etching resist layer having a prescribed pattern onthe Cu plating layer and etching away those portions of the Cu platinglayer which are exposed from the etching resist layer. As a result ofthe execution of this step, the first and second outer electrode layers6 and 7, the metal foil 2, and the first and second conductor layers 4and 4′ are electrically connected to each other and a capacitor 10 isthereby completed. Alternatively, the conductor layer M3, which willbecome a first outer electrode layer 6 on the insulating resin layer 16(V2 b), may be formed by a semi-additive method in which Cu electrolessplating is performed first, a plating resist layer is formed in aprescribed pattern, Cu electroplating is then performed, portions of theplating resist layer are peeled off, and finally theplating-resist-layer-peeled portions of the Cu electroless plating layerare etched away.

The remaining part of a first wiring lamination portion L1 consisting ofan insulating resin layer 16 (V3) and a conductor layer M4, a solderresist layer 18, etc. are laid one on another by a known build-upmethod, whereby a wiring board 100 is completed (see FIG. 4).

For example, the capacitor 10 can be mounted inside the first wiringlamination portion L1 according to the following procedure. First, thedielectric lamination structure 1 is put on an insulating resin layer 16(V2 a) formed on a board core 12. Then, an insulating resin layer 16 (V2b) is laid on the dielectric lamination structure 1 and pressure isexerted on them while they are heated. As a result, portions of theinsulating resin films 16 (V2 a and V2 b) flow laterally to thedielectric lamination structure 1, whereby the dielectric laminationstructure 1 is placed within the thickness of the insulating resinlayers 16. Then, via holes 8 h and 9 h are formed through the insulatingresin layers 16 (V2 a and V2 b) right above a conductor layer M2. Viaconductors 34 are formed so as to be connected to conductor layers inthe via holes 8 h and 9 h, whereby a capacitor 10 is completed. The viaconductors 34 can be formed by using a via paste which will become viaconductors 34 after thermal setting or by plating. Subsequently, aninsulating resin layer 16 (V3) is formed on the capacitor 10.

Next, another embodiment of the invention will be described withreference to the accompanying drawings. In the following configuration,members having the same functions as corresponding members of the aboveembodiment will be given the same symbols as the latter and will not bedescribed in detail.

FIG. 8 is a schematic diagram of a capacitor 50 according to another(second) embodiment of the invention. As shown in FIG. 8, the capacitor50 is provided with a dielectric lamination structure 1 (core member),insulating resin layers 16 and 17 which cover the dielectric laminationstructure 1, a first outer electrode layer 6 formed on a first majorsurface 50 a of the capacitor 50, a second outer electrode layer 7formed on a second major surface 50 b of the capacitor 50, viaconductors 8 a, 8 b, and 8 c which penetrate through the capacitor 50 inthe thickness direction and electrically connect the first and secondouter electrode layers 6 and 7, via conductors 9 which penetrate throughthe insulating resin layer 16 from the first major surface 50 a to thefirst conductor layer 4 and electrically connect the first outerelectrode layer 6 and the first conductor layer 4, a lower electrodelayer 20 formed between the lower insulating resin layers 16 and 17which are disposed under the dielectric lamination structure 1, and viaconductors 19 which electrically connect the lower electrode layer 20and the second conductor layer 4′. The second conductor layer 4′ iselectrically connected to the via conductor(s) 8 b via the lowerelectrode layer 20 and the via conductors 19.

The capacitor 50 can provide a sufficient capacitance because it iscomposed of the metal foil 2, the first and second dielectric layers 3and 3′ which are formed on both of the front and back surfaces of themetal foil 2, and the first and second conductor layers 4 and 4′. Theplural via conductors 19 are provided for the second conductor layer 4′in array form. Like the above-described capacitor 10, the capacitor 50can be incorporated in the first wiring lamination portion L1 of thewiring board 100. A manufacturing process of the capacitor 50 will bedescribed below.

FIGS. 9-11 are explanatory diagrams showing a manufacturing process ofthe capacitor 50 according to the second embodiment of the invention.First, as shown in FIG. 9 (9-1), a dielectric lamination structures 1 ismanufactured and insulating resin layers 16 are formed by laminatingsheets made of a thermosetting resin composition, for example, on thedielectric lamination structures 1 (see FIG. 9 (9-2)). Then, after theinsulating resin layers 16 are half set, as shown in FIG. 9 (9-3) viaholes 19 h are formed through the lower insulating resin layer 16 bylaser light at prescribed positions (i.e., in array form for the secondconductor layer 4′).

Then, via conductors 19 are formed by filling the insides of thethus-formed via holes 19 h by Cu plating or the like as shown in FIG. 9(9-4), and a lower electrode layer 20 is formed in a prescribed pattern(see FIG. 10 (10-1)). More specifically, the insides of the via holes 19h and the surface of the insulating resin layer 16 are subjected firstto Cu electroless plating and then to Cu electroplating. Then, viaconductors 19 and a lower conductor layer 20 are formed by forming anetching resist layer having a prescribed pattern on the Cu plating layerand etching away those portions of the Cu plating layer which areexposed from the etching resist layer. As a result of the execution ofthis step, the second conductor layer 4′ and the lower electrode layer20 are electrically connected to each other by the via conductors 19.

Then, as shown in FIG. 10 (10-2), a lamination body 51 having thethus-formed lower electrode layer 20 is mounted at a prescribed positionin the first wiring lamination portion L1 of a wiring board 100 whichwas formed by a known build-up method, for example. More specifically,in an in-process wiring board 100, an insulating resin layer 16 (V1),via conductors 34, and a conductor layer M2 are formed by a knownbuild-up method. At this time, the conductor layer M2 is formed in aprescribed pattern so that it will become a second outer electrode layer7 of a capacitor 50 when the dielectric lamination structure 1 ismounted. Then, an insulating resin layer 16 (V2 a) made of athermosetting resin composition or the like is formed on the insulatingresin layer 16 (V1) and the conductor layer M2. Then, as shown in FIG.10 (10-3), the lamination body 51 is mounted on the insulating resinlayer 16 (V2 a) by a mounter (not shown). If necessary, a heightadjustment is made as appropriate by forming an insulating resin layer16 or the like on or around the lamination body 51.

Then, as shown in FIG. 11 (11-1), via through-holes 8 h and 9 hextending in the thickness direction are formed through the insulatingresin layers 16 and 17 at prescribed positions by laser light.

Subsequently, as shown in FIG. 11 (11-2), via conductors 8 and 9 areformed by filling the insides of the thus-formed via holes 8 h and 9 hby Cu plating or the like and a conductor layer M3, which will become afirst outer electrode layer 6, is formed in a prescribed pattern. Morespecifically, the insides of the via holes 8 h and 9 h and the surfaceof the insulating resin layer 16 (V2 b) are subjected first to Cuelectroless plating and then to Cu electroplating. Then, via conductors8 and 9 and a conductor layer M3 including a first outer electrode layer6 are formed by forming an etching resist layer having a prescribedpattern on the Cu plating layer and etching away those portions of theCu plating layer which are exposed from the etching resist layer. As aresult of the execution of this step, the first and second outerelectrode layers 6 and 7, the metal foil 2, and the first and secondconductor layers 4 and 4′ are electrically connected to each other and acapacitor 50 is thereby completed.

The remaining part of a first wiring lamination portion L1 consisting ofan insulating resin layer 16 and a conductor layer M4, a solder resistlayer 18, etc. are laid one on another by a known build-up method,whereby a wiring board 100′ is completed (see FIG. 4). The capacitor 50is somewhat different in structure from the capacitor 10 which isincorporated in the wiring board 100 of FIG. 4 and which includes thedielectric lamination structure 1 of the above-described embodiment theonly one side portion of which is used to form the capacitor 10.However, the capacitor 50 can be incorporated in the wiring board 100′according to the same procedure as the capacitor 10 is incorporated inthe wiring board 100.

In the embodiments, the manufacturing method of the dielectriclamination structure 1 is such that the through-holes 2 a are formedbefore the first and second dielectric layers 3 and 3′ are formed on themajor surfaces of the metal foil 2. Therefore, the first and seconddielectric layers 3 and 3′ are not exposed to an etching liquid. Thiscan reduce the degree of damage of the first and second dielectriclayers 3 and 3′, and hence can suppress reduction in the insulationresistance of the first and second dielectric layers 3 and 3′, peelingor the like of the first and second dielectric layers 3 and 3′ off themetal foil 2, and other undesired phenomena. FIG. 14A is a photographshowing the state of the side surface of a through-hole of a pre-firingmetal foil used in the embodiment, and FIG. 14B is a photograph showingthe state of the side surface of a through-hole of a post-firing metalfoil used in the embodiment. Where the through-holes 2 a are formedbefore the first and second dielectric layers 3 and 3′ are formed on themajor surfaces of the metal foil 2, since firing is performed in a statethat the through-holes 2 a are formed in the metal foil 2, the sidesurfaces 2 a ₁ of the through-holes 2 a are roughened by the etching(see FIG. 14A) but are then flattened by the firing (see FIG. 14B)because metal particles of the metal foil 2 grow (combined with eachother) during the firing. The side surfaces 2 a ₁ of the through-holes 2a are also flattened in the above-described manner even in the casewhere the through-holes 2 a are formed by etching in a state that thefirst and second dielectric layers 3 and 3′ are formed on the majorsurfaces of the metal foil 2 and firing is performed thereafter.However, in this case, the first and second dielectric layers 3 and 3′are corroded by an etching liquid and thereby damaged. Therefore, if theside surfaces 2 a ₁ of the through-holes 2 a are flattened and the firstand second dielectric layers 3 and 3′ are not damaged much, it can bejudged that the through-holes 2 a were formed before the first andsecond dielectric layers 3 and 3′ were formed on the major surfaces ofthe metal foil 2.

Where the through-holes 2 a are formed through the metal foil 2 in astate that at least one of the metal foil 2, the first and seconddielectric layers 3 and 3′, and the first and second conductor layers 4and 4′ is buried in a wiring board, firing should be performed in astate that it is buried in the wiring board. However, it is difficult toheat the wiring board to a firing temperature. In contrast, in theembodiments, since the through-holes 2 a are formed through the metalfoil 2 in a state that none of the metal foil 2, the first and seconddielectric layers 3 and 3′, and the first and second conductor layers 4and 4′ are buried in the wiring board 100 or 100′, firing can beperformed in a state that the dielectric lamination structure 1 is notburied in the wiring board 100 or 100′. The wiring boards 100 and 100′incorporating the respective capacitors 10 and 50 can thus bemanufactured.

If firing is performed in a state that the first dielectric layer 3 andthe first conductor layer 4 are formed on only one major surface of themetal foil 2, deformation such as a warp or an undulation may occur inthe dielectric lamination structure 1 at the time of sintering becausealmost no contraction occurs in the metal foil 2 at the time ofsintering whereas the first dielectric layer 3 is sintering-contracted.Where the first dielectric layer 3 and the metal foil 2 are differentfrom each other in thermal expansion coefficient, deformation such as awarp or an undulation may occur in the dielectric lamination structure 1due to the difference in thermal expansion coefficient particularly whenthe temperature of the first dielectric layer 3 decreases after thesintering. This makes it difficult to incorporate the dielectriclamination structure 1 into a wiring board. If it is attempted toforcibly incorporate the dielectric lamination structure 1 into a wiringboard, cracks may develop in the first dielectric layer 3. In contrast,in the embodiments, since the first and second dielectric layers 3 and3′ and the first and second conductor layers 4 and 4′ are formed on bothmajor surfaces of the metal foil 2, deformation such as a warp or anundulation is not prone to occur in the dielectric lamination structure1 at the time of sintering. This allows the dielectric laminationstructure 1 to be incorporated into the wiring board 100 or 100′ easily.Furthermore, since the first and second dielectric layers 3 and 3′ andthe first and second conductor layers 4 and 4, are formed on both majorsurfaces of the metal foil 2, an about two times larger capacitance canbe obtained than in the case where the first dielectric layer 3 and thefirst conductor layer 4 are formed on only one major surface of themetal foil 2.

A manufacturing process of the dielectric lamination structure 1 whichis different from the manufacturing process described above withreference to FIG. 5 will be described below with reference to FIGS. 15A,15B and 15C.

First, through-holes 2 a are formed through a metal foil 2. On the otherhand, conductor layers 4 and 4′ are pressure-bonded to respectivedielectric layers 3 and 3′. As a result, as shown in FIG. 15A, theconductor layers 4 and 4′ are formed on the respective dielectric layers3 and 3′.

Then, as shown in FIG. 15B, each set of vias 3 a and 4 a is formedsimultaneously through the dielectric layer 3 or 3′ and the conductorlayer 4 or 4′ by laser light. The side surface of each via 4 a isretreated from the corresponding via 3 a.

After the vias 3 a and 4 a have been formed through the dielectriclayers 3 and 3′ and the conductor layers 4 and 4′, the dielectric layers3 and 3′ and the conductor layers 4 and 4′ are positioned with respectto the metal foil 2 so that the vias 3 a and 4 a communicate with therespective through-holes 2 a. And the dielectric layers 3 and 3′ and theconductor layers 4 and 4′ are pressure-bonded to the major surfaces ofthe metal foil 2 through which the through-holes 2 a are formed. As aresult, as shown in FIG. 15C, the dielectric layers 3 and 3′ and theconductor layers 4 and 4′ are formed on the major surfaces of the metalfoil 2. Then, the same steps including firing as described above areexecuted, whereby a dielectric lamination structure is obtained which isthe same as the dielectric lamination structure 1 shown in FIG. 1.

EXAMPLES

The following experiment was carried out to confirm the advantages ofthe invention.

(1) Formation of Barium Titanate (BT) Green Sheet

First, a prescribed dispersant and plasticizer were added to a BT powderof 0.7 μm in average particle diameter and they were subjected to wetmixing in a mixed solvent of ethanol and toluene. After sufficientmixing, a binder was added and mixing was performed further. Then, a7-μm thick BT green sheet was formed by a general-purpose method such asa doctor blade method by using resulting slurry.

(2) Formation of Nickel Green Sheet

A 7-μm thick nickel green sheet was formed by mixing a nickel powder of0.4 μm in average particle diameter with a barium titanate powder at avolume ratio of 7:3 by a method similar to the method of item (1).

(3) Manufacture of Dielectric Lamination Structure

A 30-μm thick nickel foil was cut into 150-mm-square sections byetching, and through-holes were formed through them. Each of the BTgreen sheet and the nickel green sheet was also cut into 150-mm-squaresections. Then, after BT green sheets were laid on both surfaces of anickel foil, the former were pressure-bonded to the latter under theconditions of 80° C. and 500 kgf/cm². After PET (polyethyleneterephthalate) carrier sheets were peeled off the respective BT greensheets, nickel green sheets were laid on the surfaces of the respectiveBT green sheets and the former were pressure-bonded to the latter underthe conditions of 80° C. and 750 kgf/cm² (main pressure bonding). WithPET carrier sheets kept stuck to the respective nickel green sheets,through-holes were formed through both BT green sheets and both nickelgreen sheets by laser light at the same positions as the through-holesof the nickel foil in such a manner that the diameters of each set ofthrough-holes became larger than the diameter of the correspondingthrough-hole of the nickel foil. Then, a resulting structure was cutinto 25-mm-square sections by a general-purpose cutting machine and thecarrier sheets were peeled off, whereby unfired dielectric laminationstructures were produced. Alternatively, pressure bonding may beperformed under the conditions of 80° C. and 500 kgf/cm² after BT greensheets and nickel green sheets are laid on a nickel foil.

(4) Degreasing and Firing

An unfired dielectric lamination structure produced by the precedingstep was degreased in the air at 250° C. for 10 hours and fired in areducing atmosphere at 1,300° C. After the firing, each BT dielectriclayer and each nickel conductor layer were 4 μm in thickness.

(5) Bending Test

FIG. 12 is a schematic diagram showing a measuring method for measuringa bendable radius of curvature of the thus-produced dielectriclamination structure. Several kinds of jigs 60 whose pressing surfaces60 a have various radii R of curvature were produced. Each jig 60 waspressed against the dielectric lamination structure until the surface ofthe dielectric lamination structure conformed to the pressing surface 60a, and the radius R of curvature of the jig 60 used was measured. Abendable radius R of curvature was determined afterwards on the basis ofwhether or not the dielectric lamination structure was broken.

In Example, the test result was such that the jigs 60 whose pressingsurfaces 60 a had radii R of curvature of 5 mm or more were able to bendthe dielectric lamination structure. It is known that not a low degreeof bend (radius of curvature: about 500 mm) occurs in a capacitor duringa manufacturing process. Therefore, it can be said that a capacitor thatcan be deformed in a radius-of-curvature range of 5 to 500 mm wasobtained. That is, a capacitor which is rigid enough to endure a warp inthe above range was obtained. No reduction in capacitance was found in athermal shock test.

(6) Mounting on Wiring Board

An insulating resin film was laminated on a wiring board that wasmanufactured by a known process. The dielectric lamination structure wasmounted on the insulating resin film at a prescribed position with amounter and the insulating resin film was set tentatively (roughened).

(7) Manufacture of Capacitor-Incorporated Board

An insulating resin film was laminated on the dielectric laminationstructure, vias were formed at prescribed positions by laser light, andCu plating was performed, whereby a capacitor having an array structurewas formed. Then, a capacitor-incorporated board was completed by aknown build-up process.

(8) Reliability Evaluation (Thermal Shock JESD 22-A106B (JEDECStandard))

The thus-manufactured capacitor-incorporated board was subjected to athermal shock test in which it was immersed alternately in a liquid tankof −50° C. and a liquid tank of +50° C. (1,000 cycles) Capacitancevalues before and after the test were measured. No change was foundbetween the capacitance values measured before and after the test.

(9) Peeling Test

After an insulating resin film was laminated on a wiring board, thedielectric lamination structure was mounted on the insulating resin filmat a prescribed position with a mounter. Then, the resin was set byheating. Then, the dielectric lamination structure was subjected to apeeling test. It was found that strong force was necessary to peel offthe dielectric lamination structure and hence the dielectric laminationstructure could not be peeled off easily. An observation of the place,from which the dielectric lamination structure was peeled off, found noair bubble marks.

A dielectric lamination structure of Comparative Example 1 wasmanufactured in the same manner as described above by using a 100-μmthick nickel foil and a 30-μm thick BT green sheet. Being thick, thedielectric lamination structure of Comparative Example 1 was broken(e.g., cracks developed) when the jigs were pressed against it.Furthermore, reduction in capacitance occurred in a thermal shock test.

Dielectric lamination structures and wiring boards of ComparativeExamples 2 and 3 were manufactured by manufacturing methods that weredifferent from the manufacturing method of Example.

In Comparative Example 2, an Ni foil (metal foil), barium titanate greensheets (dielectric layers), Ni paste layers (conductor layers) were usedand a dielectric lamination structure was manufactured in which bariumtitanate layers and Ni layers were formed on an Ni film. And a wiringboard incorporating a dielectric lamination structure was manufacturedby using the thus-manufactured dielectric lamination structure.

More specifically, vias were formed in barium titanate green sheets bylaser light in advance at positions corresponding to through-holes ofthe Ni foil. The barium titanate green sheets were positioned withrespect to the Ni foil and pressure-bonded to the latter. Then, Ni pastelayers were formed on the barium titanate green sheets by screenprinting. The other conditions were the same as in Example.

In Comparative Example 3, an Ni foil (metal foil), barium titanate greensheets (dielectric layers), Ni paste layers (conductor layers) were usedand a dielectric lamination structure in which barium titanate layersand Ni layers were formed on an Ni film was manufactured. And a wiringboard incorporating a dielectric lamination structure was manufacturedby using the thus-manufactured dielectric lamination structure.

More specifically, vias were formed in barium titanate green sheets bylaser light in advance at positions corresponding to through-holes ofthe Ni foil. The barium titanate green sheets were positioned withrespect to the Ni foil and pressure-bonded to the latter. Then, Ni pastelayers were formed on the barium titanate green sheets by screenprinting. However, in Comparative Example 3, to prevent the Ni pastelayers from going into the vias of the barium titanate green sheets, aprinting mask was used which makes the length of retreat of the sidesurfaces of the vias of the Ni paste layers from those of the vias ofthe barium titanate green sheets greater than in Comparative Example 2.

The portions of the Ni layers in the vicinities of the vias of thebarium titanate layers of the above-described dielectric laminationstructure of each of Comparative Examples 2 and 3 were observed andlengths of retreat of the side surfaces of the vias of the Ni pastelayers from those of the vias of the barium titanate layers weremeasured.

In Comparative Example 2, portions of the Ni layers went into the viasof the barium titanate layers, whereby the Ni foil and the Ni layerswere short-circuited with each other. On the other hand, in ComparativeExample 3, since the length of retreat was 60 μm which was too great,the capacitance of the capacitor was out of an allowable range. Also inExample, since the side surfaces of the vias of the Ni layers wereretreated, the capacitance of the capacitor was reduced accordingly.However, since the length of retreat was as short as 12 μm, thecapacitance of the capacitor was within the allowable range.

The above results show that, in Example, although vias were formedthrough the dielectric layers and the conductor layers simultaneously bylaser light in a state that the dielectric layers and the conductorlayers were formed on the metal foil, it was possible to preventshort-circuiting between the metal foil and the conductor layers and tosuppress reduction in the capacitance of a capacitor.

The invention is not limited to the above-described embodiments andExample and various modifications to those can be made in accordancewith the purpose or use without departing from the spirit and scope ofthe invention.

This application is based on Japanese Patent Application JP 2005-353791,filed Dec. 7, 2005, Japanese Patent Application JP 2006-14353, filedJan. 23, 2006, and Japanese Patent Application JP 2006-283292, filedOct. 18, 2006, the entire contents of which are hereby incorporated byreference, the same as if set forth at length.

1. A dielectric structure comprising: a metal foil; a dielectric layer;and a conductor layer provided in this order, wherein the metal foil hasa thickness of from 10 to 40 μm, the dielectric layer has a thickness offrom 0.3 to 5 μm, and the conductor layer has a thickness of from 0.3 to10 μm, the dielectric structure has plural vias which are separated fromeach other, and which penetrate through both of the dielectric layer andthe conductor layer, and the vias of the dielectric layer have differentdiameters which are in a range of from 100 to 300 μm, a diameter of eachof the vias of the conductor layer is larger than a diameter of acorresponding via of the dielectric layer by 5 to 50 μm, and a minimumvia pitch is from 100 to 350 μm.
 2. The dielectric structure accordingto claim 1, wherein the metal foil has through-holes which penetratethrough the metal foil so as to communicate with the respective vias,and a diameter of each of the through-hole is smaller than a diameter ofa corresponding via of the dielectric layer.
 3. The dielectric structureaccording to claim 1, wherein a positional deviation between a center ofeach of the vias of the dielectric layer and a center of a correspondingvia of the conductor layer is 10 μm or less.
 4. The dielectric structureaccording to claim 1, wherein the dielectric layer and the conductorlayer are provided on both sides of the metal foil so as to be arrangedsymmetrically with respect to the metal foil.
 5. The dielectricstructure according to claim 1, wherein the metal foil is an Ni foil. 6.The dielectric structure according to claim 1, wherein the conductorlayer contains 50 vol % or less of ceramic powder.
 7. The dielectricstructure according to claim 1, wherein the ceramic powder contained inthe conductor layer has same composition as ceramics contained in thedielectric layer.
 8. The dielectric structure according to claim 1,wherein the ceramic powder contained in the conductor layer containsbarium titanate.
 9. The dielectric structure according to claim 1,wherein the dielectric structure is capable of being deformed in a rangeof a radius of curvature of from 5 to 500 mm when a jig is pressedagainst the dielectric structure directly or indirectly from a side ofthe conductor layer in a state that the conductor layer is an outermostlayer.
 10. A wiring board in which the dielectric structure according toclaim 1 is incorporated, wherein the wiring board comprises aninsulating resin layer which covers the dielectric structure; and anelectrode layer and thickness-direction conductors which electricallyconnect the electrode layer and the conductor layer are provided on asurface of the insulating resin layer.
 11. A method for manufacturing adielectric structure in which the dielectric structure includes a metalfoil, a dielectric layer and a conductor layer provided in this order,vias penetrate through both of the dielectric layer and the conductorlayer, and through-holes penetrate through the metal foil so as tocommunicate with the respective vias, the method comprising: forming theconductor layer on the dielectric layer; and forming each of the vias bylaser light in such a manner that it is formed through both of theconductor layer and the dielectric layer simultaneously after theconductor layer is formed on the dielectric layer.
 12. The methodaccording to claim 11, wherein the via formation by laser light isperformed in a state that the dielectric layer and the conductor layerare formed on the metal foil.
 13. The method according to claim 11,wherein the via formation by laser light is performed before thedielectric layer and the conductor layer are formed on the metal foil.14. The method according to claim 11, wherein the dielectric layer andthe conductor layer are formed on both sides of the metal foil.
 15. Themethod according to claim 14, wherein the through-holes which penetratethrough the metal foil so as to communicate with the respective vias areformed before the dielectric layer and the conductor layer are formed onat least one side of the metal foil.